Verbal communication in interiors is often affected by a noisy background and in case of electronically amplified communication feedback effects tend to deteriorate the quality of the processed acoustic signals. A prominent example for communication in interiors is the communication of passengers in passenger compartments of automobiles. In particular, at high traveling speeds dialogs between back and front passengers are easily disturbed by background noise. If additional audio signals, e.g., from a radio or a CD player, are output during the conversation, the intelligibility of the utterances deteriorates further.
To improve the intelligibility of the passengers' utterances in-vehicle communication systems (intercom systems) comprising speech processing module are more and more commonly installed in passenger compartments. Microphones mounted near each seat of the passenger compartment can detect speech signals from the passengers. The microphone signals are processed by a speech signal processing module and output by loudspeakers. Speech signals coming from a back passenger are preferably output by front loudspeakers and vice versa.
Since the passenger compartments represent relatively small interiors, the output signals from the loudspeakers are easily fed back to the microphones, if interior communication system comprising microphones and loudspeakers are used.
Consequently, it is necessary to reduce acoustic feedback that otherwise can cause, e.g., unpleasant echoes. In the worst case, acoustic feedback can even result in a complete breakdown of communication. Reliable feedback reduction module cannot easily be designed, since the reverberating characteristics of passenger compartments are rather complex.
In addition to in-vehicle communication systems (Intercom systems) hands-free sets are commonly installed in passenger compartments. Such hands-free sets allow for convenient telephony communication with remote parties. Again, reliable echo compensation/reduction and noise reduction are mandatory for a successful communication with a sufficient intelligibility of the transmitted/received speech signals. Moreover, during a telephone call and communication that is established via the hands-free set the communication between individual passengers of the vehicle is affected.
In general, when an in-vehicle communication system is activated during a telephone call carried out via the hands-free set the performance of the hands-free set is affected by the operation of the in-vehicle communication system and vice versa. In particular, echo paths within the passenger compartment are strongly and rapidly changing due to the in-vehicle communication system and, thus, echo compensation/reduction fails or is at least insufficiently achieved to guarantee intelligibility of processed speech signals.
Therefore, there is a need for a method of a combined operation of an in-vehicle communication system and a hands-free set that does not result in a reduced quality of the processed speech signals and particularly avoids echoes in the speech signals transmitted by the hands-free set to a remote communication partner.